Periplasmic transport systems of Gram-negative bacterial are responsible for transporting a wide variety of substances, such as sugars, amino acids, peptides, anions, and other nutrients, across the cytoplasmic membrane. The bacterial transport systems are composed of a ligand-specific binding protein and a membrane-bound protein complex. The binding proteins are located in the periplasmic space, and act as receptors for a specific ligand. The glutamine permease system provides a good model for the NMR study of the essential processes of the periplasmic binding protein-dependent membrane transport. The binding protein of the system, glutamine-binding protein (GlnBP), is a monomeric basic protein, with 226 amino-acid residues and a molecular weight of 24,935 Daltons. It binds L-glutamine with a molar ratio of 1:1 at neutral pH. In order to understand the high specificity and affinity of GlnBP for its ligand as well as the detailed mechanisms of ligand recognition and binding, a solution structure of GlnBP-Gln complex is necessary. We have been working on the backbone NMR resonance assignments of GlnBP and have assigned about 95% of the residues. Now we will start working on the sidechain assignments and structure determination. H(CCO)NH and 4D NOESY experiment are expected to be run for this purpose.